1. Field of the Invention
The invention relates to a variable compression connecting rod for use with an internal combustion engine.
2. Background Art
A xe2x80x9ccompression ratioxe2x80x9d of an internal combustion engine is defined as the ratio of the volume in a cylinder above a piston when the piston is at bottom-dead-center (BDC) to the volume in the cylinder above the piston when the piston is at top-dead-center (TDC). The higher the compression ratio, the more the air and fuel molecules are mixed and compressed, thereby resulting in increased efficiency of the engine. This in turn results in improved fuel economy and a higher ratio of output energy versus input energy of the engine.
In conventional internal combustion engines, however, the compression ratio is fixed and cannot be changed to yield optimal performance. Accordingly, variable compression ratio (VCR) internal combustion engines have been developed to vary the clearance volume of a cylinder in order to achieve improved fuel economy and increased engine power performance. Such VCR engines are designed to have a higher compression ratio during low load conditions, and a lower compression ratio during high load conditions. Known techniques include using xe2x80x9csub-chambersxe2x80x9d and xe2x80x9csub-pistonsxe2x80x9d to vary the volume of a cylinder (see, for example. U.S. Pat. Nos. 4,246,873 and 4,286,552), varying the actual dimensions of all or a portion of a piston attached to a fixed length connecting rod (see U.S. Pat. No. 5,865,092), and varying the actual length of a connecting rod (see U.S. Pat. No. 5,724,863).
Other techniques include the use of eccentric rings or bushings either at the lower xe2x80x9clargexe2x80x9d end of a connecting rod or the upper xe2x80x9csmallxe2x80x9d end of the connecting rod for varying the effective length of the connecting rod or height of a reciprocating piston. U.S. Pat. Nos. 5,417,185, 5,562,068 and 5,960,750 and Japanese Publication JP-03092552 disclose devices that include eccentric rings. These eccentric ring devices, however, are undesirable in that each eccentric ring must be rotated 180 degrees before one of the desired operating modes or positions is engaged. As a result, locking of the eccentric ring in a proper position may not occur within an optimum period of time, thereby leaving the effective length of the device and consequently the compression ratio of an associated cylinder in an undesired intermediate state.
The invention addresses the shortcomings of the prior art by providing a connecting rod assembly that may be transitioned quickly and reliably between two or more compression modes without requiring rotation of an eccentric ring member about a crankpin or wrist pin.
The connecting rod assembly of the invention is configured to vary a compression ratio of an internal combustion engine having a crankshaft and a piston. The connecting rod assembly includes a first portion adapted to be connected to the crankshaft, and a second portion adapted to be connected to the piston and movable with respect to the first portion. The connecting rod assembly further includes a locking mechanism disposed between the first and second portions. The locking mechanism includes a rotatable locking element that is configured to lock the second portion at a first position relative to the first portion. Furthermore, the first position corresponds to a first compression ratio of the engine.